We have observed that activated cells synthesize an soluble form of the Qa2 molecule. This molecule is not derived from cell surface forms. Interestingly, the cell surface Qa2 is attached to the cell surface by a phospholipid anchor. We propose a series of biochemical studies to examine both the structure of the membrane anchor and the synthesis and assembly steps of the Qa2 molecule. The biosynthetic pathway will be analyzed in both resting and activated T cells, as well as Q7 gene transfected cells, to determine if variation in assembly can account for the synthesis of soluble Qa2 molecules. In addition, studies will be initiated to determine if the relationship between specific stages in T cell activation and Qa2 secretion. Utilizing a battery of anti Qa2 reagents, we have identified two serologically distinct subpopulations of Qa2 molecules expressed on the surface of activated T cells. A detailed structural characterization of these two populations is proposed in order to determine if these two molecules represent different post- translational products or are distinct at the primary structural level. In an effort to understand the relationship between Q-region gene products and serologically defined lymphocyte specific, Qa2 subregion proteins, a biochemical analysis of the cell surface and secreted products of transfected Q genes will be established. Collectively, these studies seek to gain insights into the structure and expression of class I molecules encoded or controlled by the Qa2 subregion. This information will form the basis for future studies aimed at addressing the biological significance and function of this novel family of MHC encoded proteins.